belt printing press as shown in FIG. 1 which provides a desired printing length adjustable independently of the circumference of a plate cylinder is in use in the printing industry. In such a printing press, an endless belt 14 of a flexible resin film is reeved on a plate cylinder 10 and a tension roller 12 is movable toward or away from the plate cylinder 10 so as to adjust the distance between the axes of the cylinder and roller. A printing plate 16 is bonded on the film belt 14. An impression cylinder 18 is disposed in conjunction with the plate cylinder 10, and a continuous web of paper or the like 20 is passed between the two cylinders 10 and 18 while being pressed by both printing plate 16 and impression cylinder 18, thus printing the material 20.
In the belt printing press, a printing plate must be bonded in position on a flexible base film with strict accuracy. Heretofore, however, the location of a printing plate has been manually marked on a base film for the bonding thereof in position. The manual marking operation has been made based on the operator's skill acquired through long experience and his technical intuition, thus requiring a long period of time to determine the exact location of a printing plate which has been one of the major stumbling blocks to better efficiency in the printing preparations. Furthermore, for a multi-color printing, once a first-color printing plate has been bonded in position on its base film, the other printing plates (that is, the second-color printing plate, the third-color printing plate, and the like) that will follow must be bonded on their respective base films with reference to the location of the preceding printing plate so that no color shift occurs in the actual printing. Heretofore, however, each printing plate has been bonded without any regard to the positions of the other printing plates on their base films, often resulting in a color shift in multi-color printing.